Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!wuarchive!zaphod.mps.ohio-state.edu!rpi!uupsi!rodan.acs.syr.edu!wwtaroli From: wwtaroli@rodan.acs.syr.edu (Bill Taroli) Newsgroups: comp.sys.mac.system Subject: Re: True Multitasking Message-ID: <1991Jan16.005818.3521@rodan.acs.syr.edu> Date: 16 Jan 91 00:58:18 GMT References: Organization: Syracuse University, Syracuse, NY Lines: 47 In article kkirksey@eng.auburn.edu (Kenneth B. Kirksey) writes: >Can somebody please tell me why Apple has yet to implement TRUE multitasking >in the system software? I know that it's really not that hard of a task, >especially since the amiga has had it for quite some time. Is there a valid >reason for not doing it? I'm really curious I think you've used just about one of the most vague terms in the comuting world. Multitasking, in the most general sense, simply means being able to get your computer to run multiple programs at the same time. MultiFinder does indeed do this, but (as with anyting) there are drawbacks. MF employs cooperative multitasking. This means that all applications must abide by one set of rules (Apple's) to ensure that everyone gets times to process. However, another serious problem (not specific to MF) in the Mac OS is that there is no memory protection between applications. Thus, if our two programs are running, and mine wants to write in your address space, it can do so without any problem whatsoever. Most other systems (esp. Unix) employ preemptive multitasking. This simply means that the OS is responsible for the scheduling of tasks. Depending upon the power of the machine, this can degrade performance of applications and result in sluggish user reponse (two reasons Apple may have chose not to go this route). Bringing up the Amiga is a real interesting thing here since there are many claims that multitasking is implemented primarily in hardware on that system. Although there are different chips specialize for different tasks (something Apple has yet to do effectively, in my opinion), this would neither support multitasking OR any form of parallelism in and of itself. Without support from the OS level for preemptive MT, the Amiga simply would not have the capability. It's difficult not to start comparing hardware in these cases, but it should recognized that hardware is _not_ the source of multitasking... it is software (the OS, or the Appls). Thus, in a broad sense, the answer to your query is that the Mac already does multitasking. It just doesn't do it the same way as the Amiga. There is really no claim one way or the other which is best, as circumstances may cause one to perform better than the other. So, Apple's decision to the MF route (although possibly due to minimal work on their part) was based on the overal goals of the interface (quick response to user events, and giving priority to the foreground application). -- ______ Bill Taroli -- Syracuse University | "The only thing necessary for \ PT / | the triumph of evil is for \ / Internet: wwtaroli@rodan.acs.syr.edu | good men to do nothing." \/ BITNET: wwtaroli@sunrise.acs.syr.edu | -- Edmund Burke